Aromatic polyamide compositions and fibers

ABSTRACT

The disclosed invention relates to novel aromatic polyamide compositions with a fullerene component and fibers therefrom which have improved torsional strength and a process for preparing said fibers.

BACKGROUND OF THE INVENTION

This invention relates to polymeric compositions of aromatic polyamideswith a fullerene component, and fibers therefrom which have improvedtorsional strength and a process for preparing said fibers.

Since the isolation of fullerenes by Kratschmer et al., Nature, Vol.347, pp. 354-358 (1990), the chemistry surrounding fullerenes has beenthe focus of intense research. Fullerenes have been studied per se andin combination with other substances with the goal of modifying theproperties of the resulting compositions.

Copending, commonly assigned, application Ser. No. 07/954,181 describesthe use of fullerenes to provide improved photoconductive compositionsfrom both photoconductive and non-photoconductive polymers.

The present invention is directed to providing aromatic polyamides andfullerence compounds which form fibers having improved processabilityand compression strength as measured by torsional modulus. Of particularcommercial importance are aromatic polyamides, processed as fibers,which have uses such as: in composites, cut-resistant gloves, clothes,and cables.

SUMMARY OF THE INVENTION

The present invention provides aromatic polyamide compositions andfibers therefrom of improved torsional strength comprised of an aromaticpolyamide, and from about 0.1 to about 20% by weight, based on theweight of the polyamide, of a fullerene compound. Also comprehended bythis invention is a process for preparing an aromatic polyamide fiberwith improved torsional strength, comprising in-situ polymerization ofaromatic polyamide in the presence of fullerene compound to incorporatean "effective" amount of the fullerene.

DETAILS OF THE INVENTION

Fibers prepared from the polymeric composition of the present inventionhave improved torsional strength as compared to un-doped polyamides andas measured by torsional modulus.

Torsional modulus, τ, is defined as: ##EQU1## where D and ρ are thedenier and the density of the fiber, respectively. Torsional modulus ofthe fiber can therefore be determined by measuring the initial slope ofa plot of torque versus angle of twist. Angle of twist versus torquemeasurements can be done on fibers with different denier, and theresults are substituted into equations (1) and (2) to obtain torsionalmodulus.

There is usually a correlation between torsional strength andcompression strength. Improving the torsional strength of a materialcan, although not always, also improve the compression strength.

Fullerene compounds of the present invention include fullerenes in thesubstituted and unsubstituted form. The terms fullerene and fullerenecompound are herein used interchangeably.

The fullerene compound useful in the compositions and fibers of thisinvention can be made by the procedure described by Kratschmer et al.,Nature 347-354 (1990). The fullerenes useful in this invention may havean extremely broad range of carbon atoms. Useful fullerene compounds mayhave 20-1000 carbon atoms, or mixtures thereof, preferably fullerenecompounds having 60 or 70 carbon atoms, or mixtures thereof, but can beany stable form of the fullerene as described in Zhang et al., J. Phys.Chem. Vol. 90, p. 525 (1986); Newton et al., J. Am. Chem. Soc., Vol.108, p. 1469 (1984); Fowler, Chem. Phys. Lett., Vol. 131, p. 444-450(1986). It is also permissible to utilize any substituted form offullerene, so long as the substitution is such that the electronaccepting character of the molecule remains in tact. Fullerene compoundsobtained in accordance with the methods set forth in Kratschmer et al.,may contain mixtures of C₆₀ and C₇₀ and small amounts of impurities.

The concentration of fullerene in the compositions of the presentinvention is from about 0.1 to about 20% by weight, preferably 0.1 toabout 5% by weight, more preferably less than 5% by weight of aromaticpolyamide.

Methods of preparation wherein fullerenes can be incorporated (i.e.,doped) into these aromatic polyamides include: (i) in-situpolymerization, (ii) dissolving both fullerenes and polyamide in acommon solvent, or (iii) where the polyamide melts upon heating ratherthan decomposing, one may dissolve the fullerene into the polyamidemelt. Method (i) is preferred (Example 1) particularly for incorporationof higher amounts of fullerene into the composition, wherein fullereneis added to the monomeric precursor of the aromatic polyamide. Fiberscan be prepared from the resulting compositions described below.

Examples of common solvents for use in method (ii) include:N-methylpyrrolidone (NMP), Dimethylacetamide (DMAC), andDimethylformamide (DMF).

Many aromatic polyamides are used in the form of fibers and films. Thefiber can mean finite length or continuous, single filament or yarn andthe yarn can be monofilament or multifilament yarn. Fibers may be formedby wet spinning of an aromatic polyamide solution, while films may beformed by casting a thin layer of the aromatic polyamide solution. Inboth cases, the aromatic polyamide solution is usually contacted with anonsolvent such as water, which removes the solvent swelling thearomatic polyamide and hence coagulates the aromatic polyamide into asolid polymer, for example as a fiber or film creating a solvent swollenaromatic polyamide. Hence in this type of process the water is oftencalled a coagulant. A convenient method of contacting the solventswollen aromatic polyamide with a solution of a fullerene compound, isthe use of a fullerene containing solution as the coagulant in theprocess of forming fibers and films. Another convenient method ofcontacting the aromatic polyamide with a fullerene solution is tocontact a "never dried" aromatic polyamide with the fullerene solution.

A "never dried" aramid means an aramid coagulated from a solution bycontact with a nonsolvent (usually an aqueous bath of some sort, such aswater or an aqueous solution). When contacted with the nonsolvent, thepolymer coagulates and most of the solvent is removed structure, whichusually contains about 150-200% by weight of the aramid of nonsolvent(again, usually water). It is this open sponge-like structure, which hasimbibed the nonsolvent, which is referred to herein as "never driedaramid".

The aromatic polyamide is then dried to produce the final article (fiberor film). Drying is typically done by the removal of excess water andaromatic polyamide solvent mechanically, and then the removal of theresidual water and solvent by vaporization, as by heating. Typical wetfiber spinning procedures for aromatic polyamides are known to the artskilled and are described in H. Mark, et al., Ed., Encyclopedia ofPolymer Science and Technology, Vol. 6, John Wiley & Sons, New York,1986, pp. 802-839, which are hereby included by reference.

Aromatic polyamides particularly useful herein includepoly(p-phenyleneterephthalamide), and poly(m-phenyleneisophthalamide)because of their proven utility for bullet-proof vests, engineeringcomposites, fire proof apparel, cut resistant gloves, cables and thelike.

End uses for the fibers of improved torsional strength include:composites, cut-resistant gloves, fire resistant clothes, and cables.

In the Examples, the following abbreviations are used:

MPD-I--poly(m-phenylene isophthalamide) (Nomex®)

PPD-T--poly(p-phenylene terephthalamide) (Kevlar®)

hrel--relative velocity

TCI--terephaloyl chloride

PPD--(p-phenylene diamine)

IV--inherent viscosity

PREPARATION OF FULLERENES

In accordance with the methods set forth in Kratschmer et al. Nature,pp. 347-354 (1990) C₆₀ and C₇₀ fullerenes are prepared. 1/8" graphiterods are evaporated in an evaporator under 150 torr of helium by passingelectrical currents of 120 amperes at 20 volts through the rods. Theblack soot generated is collected and then extracted with toluene in aSoxhlet tube to obtain fullerenes containing mixtures of C₆₀, C₇₀ andsmall amount of impurities. To separate the C₆₀ and C₇₀ fullerenes,mixtures of these fullerenes are dissolved in either hexane, 5%toluene/hexane, or 20% toluene/hexane. The resulting solution is passedthrough a column containing neutral alumina. C₆₀ (purple color) comesout of the column first, followed by C₇₀ (orange brown). The "C₆₀ /C₇₀Fullerene" utilized in Example 1 below is prepared by the electric arcmethod described above.

POLYMERIZATION OF PPD-T IN THE Presence of Fullerenes A. Preparation ofFullerene Solution in NMP

0.55 grams of C₆₀ /C₇₀ fullerene was added to 5 ml of dried NMP in asmall Erlenmeyer flask. The mixture was agitated overnight at roomtemperature in order to dissolve the fullerene in NMP. This solution waskept agitated in drybox until used for the polymerization.

B. In-situ Polymerization of PPD-T in the Presence of Fullerene

In a polymerization kettle, add (1) 75 grams of solvent premixcontaining NMP (N-methyl pyrrolidone) and CaCl₂. Percent CaCl₂(w/w):8.72%, (2) 4.663 grams of PPD (p-phenylene diamine) flake, (3)fullerene solution prepared above. Set up the kettle equipped withnitrogen inlet and outlet, an agitator, ingredient addition port, andstir until all the solid particles are completely dissolved. Place icewater bath under the kettle and cool the mixture until the temperaturereaches below 50° C. Add 8.779 grams of TCl (terephthaloyl chloride)into the reaction kettle and agitate vigorously until maximum viscosityis reached. The polymer is precipitated out as crumb in a few minutesafter the content reaches the maximum viscosity. Agitate 30 more minutesto complete the polymerization. Disassemble the kettle assembly andtransfer the polymer/fullerene blend to the "Waring Blender" and washwith 500 ml of water to remove the solvent and HCl generated by thereaction. Filter the polymer and repeat the washing four more times. Drythe polymer in convection oven for 2-3 hours at 125° C. Inherentviscosity measured in sulfuric acid was 5.47. Inherent Viscosity (IV) isdefined by the equation:

    IV=In(hrel)/c

where c is the concentration (0.5 gram of polymer in 100 ml of solvent)of the polymer solution and hrel (relative viscosity) is the ratiobetween the flow times of the polymer solution and the solvent asmeasured at 30° C. in a capillary viscometer. The inherent viscosityvalues reported and specified herein are determined using concentratedsulfuric acid (96% by weight H₂ SO₄).

EXAMPLE 2 The Preparation of PPD-T/Fullerene Fibers

Sulfuric acid having a concentration of 101% (81.5 parts) was stirredand cooled in a closed vessel to -5° C. Poly(p-phenyleneterephthalamide)/fullerene in-situ blend (19.5 parts) prepared above wasadded to the vessel. The mixture of polymer and acid was stirred whilethe temperature was gradually increased to 85° C. The mixture wasstirred for two hours at 85° C. under a reduced pressure of 25 mmHg toeliminate air bubbles. The resulting dope was extruded through a 3-holespinneret having orifice diameters of 3 mil (0.076 mm); and the extrudeddope was drawn through an air gap of 0.7 cm length into an aqueouscoagulating bath at 5° C. and wound up. The extruded dope was stretched3.5 times in one case and 7 times in the other in the air gap. Theresulting fiber was washed with dilute aqueous alkali and water, driedon a roll at 180° C., and wound up. For these fibers, the fullereneconcentration was 5.36 % based on weight of PPD-T. The color of thefibers is black as compared to the yellowish color of undoped PPD-Tfiber. The filament linear density was 4.1 denier for a stretch factorof 3.5 and 2.5 denier for a stretch factor of 7.

The torsional moduli of fullerene-doped "Kevlar" fibers are determinedto be 2.2 for the 2.5 denier fiber and 2.7 Gpascal for the 4.1 denierfiber by measuring twist angle versus torque. Compared to the torsionalmodulus of an otherwise equivalent undoped "Kevlar" fiber, 1.7 Gpascal,there is an enhancement of ˜29 to ˜59%.

Differential scanning calorimetry on the 2.5 denier fullerene-dopedKevlar fiber shows there is a significant decrease of ˜20° C. for thewater evaporation temperature compared to undoped "Kevlar" fiber.

What is claimed is:
 1. A process for preparing an aromaticpolyamide/fullerene compound fiber with improved torsional modulus,comprising in-situ polymerization of aromatic polyamides in the presenceof a fullerene compound to incorporate an "effective" amount offullerene compound into the fiber to be spun and thereafter spinningsaid polymerized mixture into a fiber.
 2. A process according to claim 1wherein the fullerene compound has from about 60 to 70 carbon atoms andis present in an amount of from about 0.1 to about 5% by weight of thepolyamide.
 3. A process according to claim 2 wherein the fullerenecompound is present in an amount of less than 5% by weight of thepolyamide.
 4. A process according to claim 2 wherein the polyamide isselected from poly(p-phenylene terephthalamide and poly(m-phenyleneisophthalamide).
 5. A process according to claim 4 wherein the polyamideis poly(p-phenylene terephthalamide) and the fullerene compound is C₆₀/C₇₀ fullerene.